All part-time employees, including substitute teachers, as well as all full-time employees hired after April 1, 1986, must pay the Medicare tax of 1.45% on total gross earnings less any pre-tax cafeteria benefits. 

The percentage taken from each paycheck effective 9/1/2021, 8.0% is deducted.  You cannot change the percentage withdrawn as this is state mandated.

This is money taken from every regular full-time and part-time employee that goes into your actual retirement account with TRS.

0.65% of gross wages 

This is what every regular full-time and part-time employee must pay each payroll that contributes towards funding the retiree medical program.